Textured microstructures in ceramic materials represent a significant departure from the traditional ceramics which have equiaxed grains. Many ceramic materials exhibit anisotropic characteristics in electronic and structural properties. Since traditional microstructures have random structure, traditional microstructures meet the requirements of most applications by averaging the anisotropic property characteristic of many ceramic crystal structures.
However, improved electronic and structural properties can be obtained if polycrystalline ceramics can be made to exhibit the anisotropic characteristics that are typical of single crystals. Such properties can be obtained if the polycrystalline body is textured.
Textured ceramics can be produced by a number of techniques including sinter forging and eutectic solidification. Another more general approach for producing textured ceramics is templated or seeded grain growth. Templated grain growth (TGG) is a technique for developing crystallographic texture in polycrystalline ceramic bodies via the grain growth of aligned template particles. In TGG, large, anisotropic particles are dispersed in a dense, fine-grained matrix. During heat treatment, the immediate environment of the template particle favors its growth. The template particles should grow until they impinge on one another or the matrix grain has coarsened enough to halt the template growth. If the template particles are oriented and grown, a textured microstructure should evolve.
Recent experiments in SiC (N. P. Padture et al., J. Am. Ceram. Soc., 77 [2] 519-23 (1994)), Si.sub.3 N.sub.4 (K. Hirao et al., J. Am. Ceram. Soc., 77 [7] 1857-62 (1994)), mullite (S. H. Hong et al., J. Eur. Ceram. Soc., 16 133-41 (1996)), and Al.sub.2 O.sub.3 (M. M. Seabaugh et al., J. Am. Ceram. Soc., 80 [5] 1181-88 (1997)) have shown oriented template particles initiate textured microstructure development.
Templates can be oriented by a variety of techniques, including tape casting, slip casting, centrifugal casting, and extrusion. In initial studies, dry forming techniques have not been used because orientation is difficult to induce during pressing of ceramic particles. Therefore, most attempts have relied on the use of colloidal processing.
Textured .alpha.-Al.sub.2 O.sub.3 -based ceramics have been made by a number of techniques. Since dielectric constant anisotropy is deleterious for alumina substrates used in the microelectronics industry, texture development in commercial tape cast alumina substrates was studied extensively in the early 1970s and means were developed to avoid it (F. V. DiMarcello, J. Am. Ceram. Soc., 55 [10] 509-14 (1972)). In 1995, Brandon et al. (Mater. Sci. Eng., A195, 189-96 (1995)) oriented .alpha.-Al.sub.2 O.sub.3 platelet particles in an .alpha.-Al.sub.2 O.sub.3 matrix in an effort to reinforce the matrix with the platelet particles. The samples demonstrated improved thermal shock resistance and inhibited crack propagation in the through-thickness direction.
Belmonte et al. (J. Mater. Sci., 29 [1] 179-83 (1994)) investigated the sintering behavior of alumina 10 powder compacts containing alumina platelet particles. The .alpha.-Al.sub.2 O.sub.3 platelet particles were shown to inhibit densification. Recently, L. An et al. (J. Mater. Res., 12 [12] 3300-3306 (1997)) combined the reaction bonding of aluminum oxide process and water-based gel casting to obtain textured alumina-platelet reinforced composites. They used tape casting as the forming process with an extended doctor blade arrangement to align template particles, and hence to produce textured specimens. Their initial composition was 45 vol. % Al, 35 vol. % .alpha.-Al.sub.2 O.sub.3, and 20 vol. % ZrO.sub.2. They sintered samples for 5 h at 1550.degree. C.
The processing of textured ceramic components by approaches described in the literature are limited by high temperature (&gt;1600.degree. C.), colloidal-based processes and subsequent part size limitations, and limited texture.
Accordingly, it is an object of the invention to provide an improved method for the manufacture of textured ceramics.